Dc link charging of capacitor in a wireless power transfer pad

ABSTRACT

An apparatus for wireless power transfer may be configured to receive power wirelessly and to output power to a load. The apparatus may include a wireless power transfer pad configured to receive power wirelessly. The apparatus may include a secondary circuit having a rectification section arranged to receive alternating current from the wireless power transfer pad and output rectified current to the load via a positive bus. The rectification section may include a first rectification device connected to the positive bus. The rectification section may include a capacitor connected between the first rectification device and a negative bus connected to the rectification section and arranged for connection to the load. Other examples may be described and claimed.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/262,717, filed on Jan. 30, 2019, which claims the benefit of U.S.Provisional Patent Application No. 62/623,777, filed on Jan. 30, 2018,each of which is incorporated herein by reference.

FIELD

This invention relates to wireless power transfer and more particularlyrelates to DC link charging of a capacitor in a wireless power transferpad.

BACKGROUND

Wireless power transfer is an emerging field and power levels haveincreased to the point that wireless power transfer is now used forwireless charging of vehicles. As power levels increase, component sizesincrease, including capacitors used for filtering and other purposes.

SUMMARY

An apparatus for wireless power transfer is disclosed. An alternateapparatus and a system perform the functions of the apparatus. Theapparatus includes a wireless power transfer (“WPT”) pad, a secondarycircuit with a rectification section that receives power from the WPTpad, a capacitor, and a first rectification device connected to thecapacitor. The capacitor and first rectification device are connected inparallel with the rectification section and in parallel with a load. Theapparatus includes a second rectification device connected to therectification section and an intermediate node between the capacitor andfirst rectification device.

Another apparatus for wireless power transfer includes a wireless powertransfer (“WPT”) pad, a secondary circuit with a rectification sectionthat receives power from the WPT pad, a capacitor, and a firstrectification device connected to the capacitor. The capacitor and firstrectification device are connected in parallel with the rectificationsection and in parallel with a load. The first rectification deviceincludes a blocking diode and the load includes a battery. The apparatusincludes a second rectification device connected to the rectificationsection and an intermediate node between the capacitor and firstrectification device, where the second rectification device includes acharging diode. The rectification section includes a full-bridgerectifier with two series-connected diodes in a first leg connectedbetween a positive bus that connects the rectification section to theload and a return and a second leg with two series-connected diodeswhere an anode of a first charging diode of the second rectificationdevice is connected between the diodes of the first leg and an anode ofa second charging diode of the second rectification device is connectedbetween the diodes of the second leg.

A system for wireless power transfer includes a power converterapparatus connected to a power source and a secondary receiver apparatusmounted to a vehicle. The secondary receiver apparatus is configured toreceive power wirelessly from the power converter apparatus with aprimary WPT pad. The secondary receiver apparatus includes a secondaryWPT pad, a secondary circuit with a rectification section that receivespower from the secondary WPT pad, a capacitor, and a first rectificationdevice connected to the capacitor. The capacitor and first rectificationdevice are connected in parallel with the rectification section and inparallel with a load of the vehicle. The secondary receiver apparatusincludes a second rectification device connected to the rectificationsection and an intermediate node between the capacitor and firstrectification device.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of the invention will be readilyunderstood, a more particular description of the invention brieflydescribed above will be rendered by reference to specific embodimentsthat are illustrated in the appended drawings. Understanding that thesedrawings depict only typical embodiments of the invention and are nottherefore to be limiting of its scope, the invention will be describedand explained with additional specificity and detail through theaccompanying drawings, in which:

FIG. 1 is a schematic block diagram illustrating one embodiment of asystem with a low voltage wireless power transfer (“WPT”) pad;

FIG. 2 is a schematic block diagram illustrating one embodiment of apower converter apparatus;

FIG. 3A is a schematic block diagram illustrating one embodiment of asecondary circuit with a rectification circuit, the secondary circuitfeeding a load;

FIG. 3B is a schematic block diagram illustrating one embodiment of asecondary circuit with a rectification section and a tuning sectionwhere the secondary circuit is feeding a load;

FIG. 4A is a schematic block diagram illustrating one embodiment of arectification section feeding a load and a coil charged direct current(“DC”) link capacitor;

FIG. 4B is a schematic block diagram illustrating another embodiment ofa rectification section feeding a load and a coil charged DC linkcapacitor; and

FIG. 5 is a graphical illustration of a rectification section currentand a load current.

DETAILED DESCRIPTION

Reference throughout this specification to “one embodiment,” “anembodiment,” or similar language means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment. Thus, appearances of the phrases“in one embodiment,” “in an embodiment,” and similar language throughoutthis specification may, but do not necessarily, all refer to the sameembodiment, but mean “one or more but not all embodiments” unlessexpressly specified otherwise. The terms “including,” “comprising,”“having,” and variations thereof mean “including but not limited to”unless expressly specified otherwise. An enumerated listing of itemsdoes not imply that any or all of the items are mutually exclusiveand/or mutually inclusive, unless expressly specified otherwise. Theterms “a,” “an,” and “the” also refer to “one or more” unless expresslyspecified otherwise.

Furthermore, the described features, structures, or characteristics ofthe invention may be combined in any suitable manner in one or moreembodiments. In the following description, numerous specific details areprovided, such as examples of programming, software modules, userselections, network transactions, database queries, database structures,hardware modules, hardware circuits, hardware chips, etc., to provide athorough understanding of embodiments of the invention. One skilled inthe relevant art will recognize, however, that the invention may bepracticed without one or more of the specific details, or with othermethods, components, materials, and so forth. In other instances,well-known structures, materials, or operations are not shown ordescribed in detail to avoid obscuring aspects of the invention.

The schematic flow chart diagrams included herein are generally setforth as logical flow chart diagrams. As such, the depicted order andlabeled steps are indicative of one embodiment of the presented method.Other steps and methods may be conceived that are equivalent infunction, logic, or effect to one or more steps, or portions thereof, ofthe illustrated method. Additionally, the format and symbols employedare provided to explain the logical steps of the method and areunderstood not to limit the scope of the method. Although various arrowtypes and line types may be employed in the flow chart diagrams, theyare understood not to limit the scope of the corresponding method.Indeed, some arrows or other connectors may be used to indicate only thelogical flow of the method. For instance, an arrow may indicate awaiting or monitoring period of unspecified duration between enumeratedsteps of the depicted method. Additionally, the order in which aparticular method occurs may or may not strictly adhere to the order ofthe corresponding steps shown.

An apparatus for wireless power transfer is disclosed. An alternateapparatus and a system perform the functions of the apparatus. Theapparatus includes a wireless power transfer (“WPT”) pad, a secondarycircuit with a rectification section that receives power from the WPTpad, a capacitor, and a first rectification device connected to thecapacitor. The capacitor and first rectification device are connected inparallel with the rectification section and in parallel with a load. Theapparatus includes a second rectification device connected to therectification section and an intermediate node between the capacitor andfirst rectification device.

In some embodiments, the first rectification device is a low impedancefor current from the capacitor to the load and a high impedance forcurrent from the load to the capacitor. In other embodiments, the firstrectification device includes a blocking diode and an anode of theblocking diode is connected to the capacitor and a cathode of theblocking diode is connected to a positive bus that connects therectification section to the load. In other embodiments, the loadincludes a battery. In other embodiments, the second rectificationdevice is a low impedance for current from the capacitor to therectification section and a high impedance for current from therectification section to the capacitor.

In some embodiments, the second rectification device includes a chargingdiode. The charging diode has a cathode connected to the intermediatenode. In other embodiments, the rectification section includes afull-bridge rectifier with two series-connected diodes in a first legconnected between a positive bus that connects the rectification sectionto the load and a return and a second leg includes two series-connecteddiodes. An anode of a first charging diode of the second rectificationdevice is connected between the diodes of the first leg and an anode ofa second charging diode of the second rectification device is connectedbetween the diodes of the second leg. In further embodiments, the diodesof the first leg and the diodes of the second leg are connected inseries with the cathode of each diode oriented toward the positive busand the WPT pad provides power to a point between each pair of diodes inthe first leg and in the second leg.

In some embodiments, the secondary circuit further includes a tuningsection with an inductor and/or a capacitor, where the tuning section isconnected between the WPT pad and the rectification section. In otherembodiments, the WPT pad includes a ferrite structure with a planarsurface and a winding wound adjacent to the planar surface where thewinding is in a spiral-type configuration. In other embodiments, the WPTpad includes one or more capacitors in series with one or more windingsof the WPT pad. In further embodiments, the WPT pad is a secondary WPTpad that receives power from a primary WPT pad positioned with a gapbetween the primary and secondary WPT pads and power is transferredwirelessly across the gap. In other embodiments, the primary andsecondary WPT pads transfer power with an alternating current (“AC”)waveform that is rectified by the rectification section.

Another apparatus for wireless power transfer includes a wireless powertransfer (“WPT”) pad, a secondary circuit with a rectification sectionthat receives power from the WPT pad, a capacitor, and a firstrectification device connected to the capacitor. The capacitor and firstrectification device are connected in parallel with the rectificationsection and in parallel with a load. The first rectification deviceincludes a blocking diode and the load includes a battery. The apparatusincludes a second rectification device connected to the rectificationsection and an intermediate node between the capacitor and firstrectification device, where the second rectification device includes acharging diode. The rectification section includes a full-bridgerectifier with two series-connected diodes in a first leg connectedbetween a positive bus that connects the rectification section to theload and a return and a second leg with two series-connected diodeswhere an anode of a first charging diode of the second rectificationdevice is connected between the diodes of the first leg and an anode ofa second charging diode of the second rectification device is connectedbetween the diodes of the second leg.

In some embodiments, an anode of the blocking diode is connected to thecapacitor and a cathode of the blocking diode is connected to a positivebus that connects the rectification section to the load and the chargingdiode has a cathode connected to the intermediate node. In otherembodiments, the diodes of the first leg and the diodes of the secondleg are connected in series with the cathode of each diode orientedtoward the positive bus and the WPT pad provides power to a pointbetween each pair of diodes in the first leg and in the second leg. Inother embodiments, the secondary circuit includes a tuning section withan inductor and/or a capacitor. The tuning section is connected betweenthe WPT pad and the rectification section.

In some embodiments, the WPT pad includes a ferrite structure with aplanar surface and a winding wound adjacent to the planar surface wherethe winding is in a spiral-type configuration. In other embodiments, theWPT pad includes one or more capacitors in series with one or morewindings of the WPT pad and the WPT pad is a secondary WPT pad thatreceives power from a primary WPT pad positioned with a gap between theprimary and secondary WPT pads and power is transferred wirelesslyacross the gap.

A system for wireless power transfer includes a power converterapparatus connected to a power source and a secondary receiver apparatusmounted to a vehicle. The secondary receiver apparatus is configured toreceive power wirelessly from the power converter apparatus with aprimary WPT pad. The secondary receiver apparatus includes a secondaryWPT pad, a secondary circuit with a rectification section that receivespower from the secondary WPT pad, a capacitor, and a first rectificationdevice connected to the capacitor. The capacitor and first rectificationdevice are connected in parallel with the rectification section and inparallel with a load of the vehicle. The secondary receiver apparatusincludes a second rectification device connected to the rectificationsection and an intermediate node between the capacitor and firstrectification device.

FIG. 1 is a schematic block diagram illustrating one embodiment of awireless power transfer (“WPT”) system 100 with a low voltage WPT pad.The WPT system 100 includes a power converter apparatus 104 and asecondary receiver apparatus 106 separated by a gap 108, and a load 110,which are described below.

The WPT system 100 includes a power converter apparatus 104 thatreceives power from a power source 112 and transmits power over a gap108 to a secondary receiver apparatus 106, which transfers power to aload 110. The power converter apparatus 104, in one embodiment, may becalled a switching power converter and includes a resonant converter 118that receives a direct current (“DC”) voltage from a DC bus 116.

In one embodiment, the power source 112 provides DC power to the DC bus116. In another embodiment, the power source 112 is an alternatingcurrent (“AC”) power source, for example from a building power system,from a utility, from a generator, etc. and the power converter apparatus104 includes a form of rectification to provide DC power to the DC bus116. For example, the rectification may be in the form of a power factorcorrection and rectification circuit 114. In the embodiment, the powerfactor correction and rectification circuit 114 may include an activepower factor correction circuit, such as a switching power converter.The power factor correction and rectification circuit 114 may alsoinclude a full-bridge rectifier, a half-bridge rectifier, or otherrectification circuit that may include diodes, capacitors, surgesuppression, etc.

The resonant converter 118 may be controlled by a primary controller120, which may vary parameters within the resonant converter 118, suchas conduction time, conduction angle, duty cycle, switching, etc. Theprimary controller 120 may receive information from sensors and positiondetection 122 within or associated with the power converter apparatus104. The primary controller 120 may also receive information wirelesslyfrom the secondary receiver apparatus 106.

The power converter apparatus 104 includes a primary pad 126 (i.e., aprimary WPT pad) that receives power from the resonant converter 118. Inone embodiment, portions of the resonant converter 118 and primary pad126 form a resonant circuit that enables efficient wireless powertransfer across the gap 108. In another embodiment, the power converterapparatus 104 includes a switching power converter that is not aresonant converter. The gap 108, in some embodiments includes an airgap, but may also partially or totally include other substances. Forexample, where the primary pad 126 is in a roadway, the gap 108 mayinclude a resin, asphalt, concrete, or other material just over thewindings of the primary pad 126 in addition to air, snow, water, etc.between the primary pad 126 and a secondary pad 128 located in thesecondary receiver apparatus 106.

The secondary receiver apparatus 106 includes a secondary pad 128 (i.e.,a secondary WPT pad) connected to a secondary circuit 130 that deliverspower to the load 110. The secondary receiver apparatus 106 may alsoinclude a secondary decoupling controller 132 that controls thesecondary circuit 130 and may also be in communication with sensorsand/or position detection 136 and wireless communications 134 coupled tothe power converter apparatus 104.

In one embodiment, the secondary receiver apparatus 106 and load 110 arepart of a vehicle 140 that receives power from the power converterapparatus 104. The load 110 may include a battery 138, a motor, aresistive load, a circuit, or other electrical load. For example, theWPT system 100 may transfer power to a portable computer, a consumerelectronic device, to an industrial load, or other portable load thatwould benefit from receiving power wirelessly.

In one embodiment, the secondary circuit 130 includes a portion ofresonant circuit that interacts with the secondary pad 128 and that isdesigned to receive power at a resonant frequency. In anotherembodiment, the secondary circuit 130 includes a power conditioningcircuit that is not a resonant circuit. The secondary circuit 130 mayalso include a rectification circuit, such as a full-bridge rectifier, ahalf-bridge rectifier, and the like. In another embodiment, thesecondary circuit 130 includes a power converter of some type thatreceives power from the resonant circuit/rectifier and actively controlspower to the load 110. For example, the secondary circuit 130 mayinclude a switching power converter. In another embodiment, thesecondary circuit 130 includes passive components and power to the load110 is controlled by adjusting power in the power converter apparatus104. In another embodiment, the secondary circuit 130 includes an activerectifier circuit that may receive and transmit power. One of skill inthe art will recognize other forms of a secondary circuit 130appropriate for receiving power from the secondary pad 128 anddelivering power to the load 110.

The resonant converter 118, in one embodiment, includes an activeswitching section coupled to a resonant circuit formed with componentsof the resonant converter 118 and the primary pad 126. The resonantconverter 118 is described in more detail with regard to FIG. 2 .

FIG. 2 is a schematic block diagram illustrating one embodiment of apower converter apparatus 104. The power converter apparatus 104 isconnected to a power source 112 and includes a power factor correctionand rectification circuit 114 connected to a DC bus 116 feeding aresonant converter 118 connected to a primary pad 126 as described withregard to the WPT system 100 of FIG. 1 .

The resonant converter 118 includes a switching module 202 and a tuningsection 204. In one embodiment, the switching module 202 includes fourswitches configured to connect the DC bus 116 to ground. Typically,switches S1 and S3 close while switches S2 and S4 are open andvice-versa. When switches S1 and S3 are closed, the DC bus 116 isconnected to a positive connection of the tuning section 204 throughinductor L1 a, and the ground is connected to the negative connection ofthe tuning section 204 through inductor L1 b while switches S2 and S4are open. When switches S2 and S4 are closed and switches S1 and S3opened, the ground is connected to the positive terminal of the tuningsection 204, and the DC bus 116 is connected to the positive connectionof the tuning section 204. Thus, the switching module 202 alternatesconnection of the DC bus 116 and ground to the tuning section 204simulating an AC waveform. The AC waveform is typically imperfect due toharmonics.

Typically, switches S1-S4 are semiconductor switches, such as ametal-oxide-semiconductor field-effect transistor (“MOSFET”), a junctiongate field-effect transistor (“JFET”), a bipolar junction transistor(“BJT”), an insulated-gate bipolar transistor (“IGBT”) or the like.Often the switches S1-S4 include a body diode that conducts when anegative voltage is applied. In some embodiments, the timing of openingand closing switches S1-S4 are varied to achieve various modes ofoperations, such as zero-voltage switching.

The tuning section 204 of the resonant converter 118 and the primary pad126 are designed based on a chosen topology. For example, the resonantconverter 118 and primary pad 126 may form aninductor-capacitor-inductor (“LCL”) load resonant converter, a seriesresonant converter, a parallel resonant converter, and the like. Theembodiment depicted in FIG. 2 includes an LCL load resonant converter.

Resonant converters include an inductance and capacitance that form aresonant frequency. When a switching frequency of the tuning section 204is at or close to the resonant frequency, voltage with the tuningsection 204 and primary pad 126 often increases to voltages levelshigher than the voltage of the DC bus 116. For example, if the voltageof the DC bus 116 is 1 kilovolt (“kV”), voltage in the tuning section204 and resonant converter 118 may be 3 kV or higher. The high voltagesrequire component ratings, insulation ratings, etc. to be high enoughfor expected voltages.

The primary pad 126 includes capacitor C3 and inductor Lp while thetuning section 204 includes series capacitor C2. Capacitors C2 and C3add to provide a particular capacitance that forms a resonant frequencywith inductor Lp. While FIG. 2 includes a series capacitor C2 in thetuning section 204 and a series capacitor C3 in the primary pad 126,other embodiments may include a single series capacitor in either thetuning section 204 or in the primary pad 126. Other embodiments mayinclude additional series capacitors, for example in the positive andreturn lines.

While FIG. 2 is focused on the resonant converter 118 and primary pad126 of the power converter apparatus 104, the secondary receiverapparatus 106 may include a secondary pad 128 and a secondary circuit130 that may also include a tuning section 204, where the inductance ofthe secondary pad 128 and capacitance of the tuning section 204 of thesecondary circuit 130 form a resonant frequency, as explained withregard to FIG. 3 . The secondary pad 128 and secondary circuit 130 havevoltage rating issues similar to the primary pad 126 and resonantconverter 118. In other embodiments, the tuning section 204 and primarypad 126 are not designed to produce a resonance, but instead conditionvoltage from the switching module 202. For example, the tuning section204 may filter out harmonic content without filtering a switchingfrequency.

FIG. 3A is a schematic block diagram illustrating one embodiment 300 ofa secondary circuit 130 with a rectification section 304, where thesecondary circuit 130 feeds a load 110. A secondary pad 128 feeds arectification section 304 in the secondary circuit 130, which feeds aload 110. In some embodiments described herein, the secondary pad 128 isreferred to as a WPT pad 128. The secondary pad 128 includes one or morewindings arranged to receive power from a primary pad 126. The secondarypad 128 may include a ferrite structure with a planar surface andwindings adjacent to the planar surface of the ferrite structurearranged in a pattern that efficiently receives power from the primarypad 126. For example, the windings may be arranged in a spiral-typeconfiguration. In one embodiment, the secondary pad 128 mirrors theprimary pad 126 that transmits power. In another embodiment, thesecondary pad 128 differs from the primary pad 126. Typically, thesecondary pad 128 includes an inductance Ls formed as a result of thewindings and the ferrite structure of the secondary pad 128. In oneembodiment, the secondary pad 128 includes two capacitors C4 a and C4 bas depicted, but the capacitors C4 a, C4 b may be combined into a singlecapacitor C4.

A rectification section 304 of the secondary circuit 130 includesdiodes, switches, or other rectification elements to convert alternatingcurrent (“AC”) power to direct current (“DC”) power. The rectificationsection 304 depicted in FIG. 3A includes a full bridge rectifier withfour diodes D1-D4. In some embodiments, the diodes D1-D4 are replacedwith active elements, such as switches, which may be used to reduceharmonics, reduce power consumption, and the like. For example, therectification section 304 may include a switching power converter thatcontrols an output voltage to the load 110. In another embodiment, thediodes are replaced with solid state devices that include arectification section. For example, the switches may be semiconductorswitches, such as a metal-oxide-semiconductor field-effect transistor(“MOSFET”), a junction gate field-effect transistor (“JFET”), a bipolarjunction transistor (“BJT”), silicon-controlled rectifiers (“SCR”), aninsulated-gate bipolar transistor (“IGBT”) or the like. The switches mayhave a lower power consumption than diodes while performing a samefunction as a diode. For example, the switches may be controlled to turnon when a diode would be forward biased and turn off when a diode wouldbe reverse biased. In addition, the switches may include a body diode.

In one embodiment, the rectification section 304 includes a full-bridgerectifier with two series-connected diodes D1, D2 in a first legconnected between a positive bus that connects the rectification section304 to the load 110 and to a return. In the embodiment, therectification section 304 includes a second leg with twoseries-connected diodes D3, D4 also connected between the positive busand the return. In another embodiment, the diodes D1, D2 of the firstleg and the diodes D3, D4 of the second leg are connected in series withthe cathode of each diode D1-D4 oriented toward the positive bus. Thesecondary pad 128 provides power to the point between each pair ofdiodes D1 and D2, D3 and D4 in the first let and in the second leg.

The load 110, in one embodiment is a battery 138. In other embodiments,the load 110 may include other components, such as a motor, a resistiveload, electronics, and the like. In one embodiment, the secondary pad128, secondary circuit 130 and load 110 are part of a vehicle 140. Inother embodiments, the secondary pad 128, secondary circuit 130 and load110 are part of a computing device, a smartphone, and the like.

FIG. 3B is a schematic block diagram illustrating one embodiment 301 ofa secondary circuit 130 with a rectification section 304 and a tuningsection 302 where the secondary circuit 130 is feeding a load 110. Asecondary pad 128 feeds a tuning section 302 within the secondarycircuit 130 and the tuning section 302 feeds a rectification section 304in the secondary circuit 130, which feeds a load 110. For theembodiments 300, 301 of FIGS. 3A and 3B, the rectification section 304receives power from the secondary pad 128, directly or from the tuningsection 302. The secondary pad 128 of the embodiment 300 of FIG. 3A orthe tuning section 302 of the embodiment 301 of FIG. 3B is connected tothe same location in the rectification section 304. In one embodiment,the secondary pad 128 includes a single capacitor C4.

The tuning section 302 includes one or more capacitors C5, C6 andinductors L2 a, L2 b that are arranged to form a resonant circuit withthe secondary pad 128 with a resonant frequency. In some embodiments,capacitor C6 is not present. In one embodiment, the resonant frequencymatches a resonant frequency of the primary pad 126 transmitting power.Typically, a resonant frequency is formed between the inductor Ls of thesecondary pad 128 and series capacitors C4 and C5 of the secondary pad128 and/or tuning section 302. In some embodiments, the secondary pad128 or the tuning section 302 include a single series capacitor C4 orC5. Other capacitors (e.g., C6) and inductors (e.g., L2 a, L2 b) mayform a low pass filter to reduce voltage ripple at the resonantfrequency. In other embodiments, a low-pass filter is included afterrectification elements in the rectification section 304. A capacitor C7is included in the embodiments described herein. One of skill in the artwill recognize other configurations of the tuning section 302 that forma resonant tank with the secondary pad 128 and pass energy to therectification section 304 or another suitable circuit.

FIG. 4A is a schematic block diagram illustrating one embodiment 400 ofa rectification section 304 feeding a load 110 and a coil charged directcurrent (“DC”) link capacitor C7. For convenience, the capacitor C7 isdepicted outside the rectification section 304. The secondary circuit130 includes a first rectification device 402 is connected to thecapacitor C7. The capacitor C7 and the first rectification device 402are connected in parallel with the rectification section 304 and inparallel with the load 110. In addition, the secondary circuit 130includes a second rectification device 404 connected to therectification section 304 and an intermediate node 406 between thecapacitor C7 and first rectification device 402.

The first rectification device 402, in one embodiment, is a lowimpedance for current from the capacitor C7 to the load 110 and a highimpedance for current from the load 110 to the capacitor C7. Forexample, the first rectification device 402 may have a diode-typefunction when the first rectification device 402 is reverse biased,impedance of first rectification device 402 increases to minimizecurrent from the load 110 to the capacitor C7. This provides aconvenient way to block inrush current to the capacitor C7 when the load110 is connected. For example, when the load is a battery 138, a switch408 may be included and when closed may provide a high inrush current tothe capacitor C7 without the first rectification device 402. Where thefirst rectification device 402 is included, the first rectificationdevice 402 essentially blocks inrush current.

In other systems, a diode may be placed in series with the load 110.However, the entire current to the load 110 passes through the diode,which causes a tremendous power loss. In a functioning 50 kilowatt(“kW”) system, the diode loss was around 1 kW. Another approach is toput a switch and resistor in parallel with the switch 408 to the load110. However, this method introduces another mechanical part thatintroduces another failure mode and the mechanical switch may fail moreoften than other solid-state parts. While a solid-state switch may beused, in larger systems and for safety reasons, a mechanical switch maybe required.

The first rectification device 402 provides a blocking function at alower power loss. Current through the first rectification device 403 istypically limited to some ripple current from the capacitor C7 towardsthe load 110.

The second rectification device 404, provides power from therectification section 304 to the capacitor C7, which may act to chargethe capacitor C7 when voltage on the capacitor C7 is low, for example atstartup. In one embodiment, the second rectification device 404 is a lowimpedance for current from the capacitor C7 to the rectification section304 and a high impedance for current from the rectification section 304to the capacitor C7. For example, the second rectification device 404may include a diode-type function for each leg of the rectificationsection 304. In one embodiment, when voltage on a leg of therectification section 304 increases, the second rectification device 404conducts current to the capacitor C7 when the voltage of the leg of therectification section 304 is above a voltage of the capacitor C7.

In some embodiments, the secondary pad 128 and secondary circuit 130provide a controllable current source so that current through the secondrectification device 404 is controlled to an appropriate level toprevent damage to the capacitor C7. As current in a leg of therectification section 304 increases, voltage rises to a level to conductcurrent through the second rectification device 404. Beneficially,pre-charging of the capacitor C7 does not depend on the load 110.

FIG. 4B is a schematic block diagram illustrating another embodiment 401of a rectification section 304 feeding a load 110 and a coil charged DClink capacitor C7. The embodiment 401 of FIG. 4B includes a blockingdiode D5 in the first rectification device 402 where the anode of theblocking diode D5 is connected to the capacitor C7 and a cathode of theblocking diode D5 is connected to a positive bus 410 that connects therectification section 340 to the load 110.

In other embodiments, the blocking diode D5 is replaced by anotherdevice that provides a blocking diode D5 function. For example, theblocking diode D5 may be replaced with a switch with a diode function ora switch that closes when the first rectification device 402 is intendedto conduct and is off when the first rectification device 402 isintended to block current from the load 110. The switches may besemiconductor switches, such as a metal-oxide-semiconductor field-effecttransistor (“MOSFET”), a junction gate field-effect transistor (“JFET”),a bipolar junction transistor (“BJT”), silicon-controlled rectifiers(“SCR”), an insulated-gate bipolar transistor (“IGBT”) or the like.

In some embodiments, the second rectification device includes a chargingdiode (e.g., D6 or D7) that has a cathode connected to the intermediatenode 406. Where the rectification section 304 is a full-bridge rectifieror has multiple legs with diodes, the second rectification device 404includes two or more charging diodes D6, D7; one for each leg in therectification section 304. Where the rectification section 304 is ahalf-bridge rectifier, the second rectification device 404 may include asingle charging diode (e.g., D6). As with the first rectification device402, the charging diode(s) D6, D7 within the second rectification device404 may be replaced by a device that includes a diode-type function thatconducts when current flows from the rectification section 304 to thecapacitor C7 and blocks current from the capacitor C7 to therectification section 304. The charging diodes D6, D7 may be replaced bya switch, such as the semiconductor switches described above.

Where the rectification section 304 is a full-bridge rectifier, asdepicted in FIG. 4B, the full-bridge rectifier includes twoseries-connected diodes D1, D2 in a first leg connected between thepositive bus 410 and a return 412 and a second leg includes twoseries-connected diodes D3, D4 connected between the positive bus 410and return 412 as shown. The diodes of the first leg D1, D2 and thediodes D3, D4 of the second leg are connected in series and the cathodeof each diode D1-D4 is oriented toward the positive bus 410 and wherethe secondary pad 128 provides power to a point between each pair ofdiodes D1, D2 and D3, D4 in the first leg and in the second leg. Ananode of a first charging diode D6 of the second rectification device404 is connected between the diodes D1, D2 of the first leg and an anodeof a second charging diode D7 of the rectification device is connectedbetween the diodes D3, D4 of the second leg.

FIG. 5 is a graphical illustration 500 of a rectification sectioncurrent 502 and a load current 504. The rectification current 502 of theillustration is the rectification section current I_(rect) of FIGS. 3Aand 3B and the load current 504 is the load current I_(load) of FIGS. 3Aand 3B. The load current 504 is depicted as a straight line, but one ofskill in the art will recognize that the load current 504 typicallyincludes some ripple. Typically, the capacitor C7 provides a low passfilter function to smooth the ripple so that the load current 504 doesnot have the same profile as the rectification section current 502.

As the rectification section current 502 rises, without the firstrectification device 402 and the second rectification device 404 currentwill flow into the capacitor C7. Voltage of the capacitor C7 changesslowly so that as voltage of the positive bus 410 rises above voltage ofthe capacitor C7, the capacitor will sink current. Energy stored in thecapacitor C7 will support current to the load 110 when voltage of thepositive bus 410 is lower than voltage on the capacitor C7.

With the first rectification device 402 and the second rectificationdevice 404 included, as depicted in FIGS. 4A and 4B, the firstrectification device 402 will block current from the positive bus 410from flowing into the capacitor C7, but when voltage at the nodesbetween the diodes of the rectification section 304 rise above thevoltage of the capacitor C7, current will flow through the secondrectification device 404 to the capacitor C7, which is represented bythe area 508 above the load current 504 and below the rectificationsection current 502. When the rectification section current 502 is belowthe load current 504, which corresponds to when voltage at the nodesbetween the diodes of the rectification section 304 is below the voltageof the capacitor C7, current will not flow through the secondrectification device 404, but current will flow from the capacitor C7through the first rectification device 402 to the load 110. The area 506below the load current 504 and above the rectification section current502 represents current flowing through the first rectification device402.

Power loss in the first rectification device 402 and the secondrectification device 404 may be less than power loss through a diode inseries with the load 110. In addition, pre-charging of the capacitor C7may be accomplished through the second rectification device 404 whileinrush current from the load 110 is blocked by the first rectificationdevice 402. Energy from the secondary pad 128 and rectification section304 can be configured as a current source, which limits current to thecapacitor C7 to prevent high inrush current.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed is:
 1. An apparatus for wireless power transfer, theapparatus configured to receive power wirelessly and to output power toa load, the apparatus comprising: a wireless power transfer (“WPT”) padconfigured to receive power wirelessly; and a secondary circuit thatincludes: a rectification section arranged to receive alternatingcurrent from the WPT pad and output rectified current to the load via apositive bus; a first rectification device connected to the positivebus; and a capacitor connected between the first rectification deviceand a negative bus connected to the rectification section and arrangedfor connection to the load.
 2. The apparatus of claim 1, furthercomprising: a second rectification device connected between therectification section and an intermediate node between the firstrectification device and the capacitor.
 3. The apparatus of claim 2,wherein: the first rectification device is forward biased between thepositive bus and the capacitor; and the second rectification device isforward biased between the rectification section and the intermediatenode.
 4. The apparatus of claim 2, wherein the second rectificationdevice includes a charging diode.
 5. The apparatus of claim 2, whereinthe second rectification device includes first and second diodes forwardbiased in parallel between the rectification section and theintermediate node.
 6. The apparatus of claim 1, wherein the firstrectification device includes a blocking diode.
 7. The apparatus ofclaim 1, wherein the secondary circuit further includes a tuning sectionthat has one or more of an inductor and a capacitor, the tuning sectionconnected between the WPT pad and the rectification section.
 8. Anapparatus for wireless power transfer, the apparatus configured toreceive power wirelessly and to output power to a load, the apparatuscomprising: a wireless power transfer (“WPT”) pad configured to receivepower wirelessly; and a secondary circuit that includes: a full-bridgerectifier arranged to receive alternating current from the WPT pad andoutput rectified current to the load via a positive bus; a firstimpedance device connected to the positive bus; and a capacitorconnected between the first impedance device and a negative busconnected to the full-bridge rectifier and arranged for connection tothe load.
 9. The apparatus of claim 8, further comprising: a secondimpedance device connected between the full-bridge rectifier and anintermediate node between the first impedance device and the capacitor.10. The apparatus of claim 9, wherein: the first impedance device has adiode-type function and is forward biased between the positive bus andthe capacitor; and the second impedance device has a diode-type functionand is forward biased between the full-bridge rectifier and theintermediate node.
 11. The apparatus of claim 9, wherein: the secondimpedance device includes a first charging diode and a second chargingdiode; the full-bridge rectifier includes two series-connected diodes ina first leg connected between the positive bus and the negative bus andtwo series-connected diodes in a second leg connected between thepositive bus and the negative bus; an anode of the first charging diodeis connected between the two series-connected diodes of the first leg;and an anode of the second charging diode is connected between the twoseries-connected diodes of the second leg.
 12. The apparatus of claim 8,wherein the secondary circuit further comprises a tuning sectioncomprising one or more of an inductor and a capacitor, the tuningsection connected between the WPT pad and the full-bridge rectifier. 13.The apparatus of claim 8, wherein: the WPT pad comprises one or morecapacitors in series with one or more windings of the WPT pad; and theWPT pad is a secondary WPT pad configured to receive power transferredwirelessly from a primary WPT pad across a gap between the primary andsecondary WPT pads.
 14. A system for wireless power transfer,comprising: a power converter apparatus that includes a primary wirelesspower transfer (“WPT”) pad configured to transfer power wirelessly; anda secondary apparatus having a secondary WPT pad configured to receivepower wirelessly from the primary WPT pad across a gap therebetween andto output power to a load, the secondary apparatus configured to bemounted to a vehicle and including: a secondary circuit that includes: arectification section arranged to receive alternating current from theWPT pad and output rectified current to the load via a positive bus; afirst rectification device connected to the positive bus; a capacitorconnected between the first rectification device and a negative busconnected to the rectification section and arranged for connection tothe load; and a second rectification device connected between therectification section and an intermediate node between the firstrectification device and the capacitor.
 15. The system of claim 14,wherein: the first rectification device is forward biased between thepositive bus and the capacitor; and the second rectification device isforward biased between the rectification section and the intermediatenode.
 16. The system of claim 14, wherein the second rectificationdevice includes a charging diode.
 17. The system of claim 14, whereinthe second rectification device includes first and second diodes forwardbiased in parallel between the rectification section and theintermediate node.
 18. The system of claim 14, wherein the secondary WPTpad includes one or more capacitors in series with one or more windingsof the secondary WPT pad.
 19. The system of claim 14, wherein the firstrectification device includes a blocking diode.
 20. The system of claim14, wherein the secondary circuit further includes a tuning section thathas one or more of an inductor and a capacitor, the tuning sectionconnected between the secondary WPT pad and the rectification section.